1.\" Copyright (c) 1990, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This code is derived from software contributed to Berkeley by 5.\" Chris Torek. 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)ffs.3 8.2 (Berkeley) 4/19/94 31.\" 32.Dd October 17, 2015 33.Dt FFS 3 34.Os 35.Sh NAME 36.Nm ffs , 37.Nm ffsl , 38.Nm ffsll , 39.Nm fls , 40.Nm flsl , 41.Nm flsll 42.Nd find first or last bit set in a bit string 43.Sh LIBRARY 44.Lb libc 45.Sh SYNOPSIS 46.In strings.h 47.Ft int 48.Fn ffs "int value" 49.Ft int 50.Fn ffsl "long value" 51.Ft int 52.Fn ffsll "long long value" 53.Ft int 54.Fn fls "int value" 55.Ft int 56.Fn flsl "long value" 57.Ft int 58.Fn flsll "long long value" 59.Sh DESCRIPTION 60The 61.Fn ffs , 62.Fn ffsl 63and 64.Fn ffsll 65functions find the first (least significant) bit set 66in 67.Fa value 68and return the index of that bit. 69.Pp 70The 71.Fn fls , 72.Fn flsl 73and 74.Fn flsll 75functions find the last (most significant) bit set in 76.Fa value 77and return the index of that bit. 78.Pp 79Bits are numbered starting at 1, the least significant bit. 80A return value of zero from any of these functions means that the 81argument was zero. 82.Sh SEE ALSO 83.Xr bitstring 3 , 84.Xr bitset 9 85.Sh HISTORY 86The 87.Fn ffs 88function appeared in 89.Bx 4.3 . 90Its prototype existed previously in 91.In string.h 92before it was moved to 93.In strings.h 94for 95.St -p1003.1-2001 96compliance. 97.Pp 98The 99.Fn ffsl , 100.Fn fls 101and 102.Fn flsl 103functions appeared in 104.Fx 5.3 . 105The 106.Fn ffsll 107and 108.Fn flsll 109functions appeared in 110.Fx 7.1 . 111